I have seen one disadvantage of using SP--it seems many special attacks using SP will execute slower than their regular attack, which can give enemies the opportunity to attack. Special attack animations also take up more time, which is probably the main reason several players have already complained about not being able to set "normal attack only" as a rule.
There are probably a few ways to make the characters ONLY attack, but here's what I did:
- Set the Party Strategy to "Conserve Resources". This sets a hard rule to not use MP or items.
- For each character, set the Action Limit rule: This is the necessary piece to control whether or not available special attacks will be used. If you set "Conserve SP up to 4" and the character has a special attack available that costs 2 SP, for example, the character will end up using the 2 SP attack when his/her SP reaches 4.
Finally, just as a tip, you can set the "Targeting Settings" for each member. "Target Same Enemy" will help the party take down the enemies, which probably helps with taking damage but will result in a slower battle compared to Suikoden's Free Will where they would generally target different/random enemies, which often allowed multiple party members to do their attacks on different targets at the same time. By targeting the same enemy, each character will wait for the previous one to finish.